1. Field of the Invention
The present invention relates to apparatus using holograms for the generation of arrays of light beamlets from a single beam input, and to the use of such apparatus to map the surface of an object.
2. Background of the Invention
Apparatus for optically generating arrays of coherent light beamlets from a single laser beam input can have wide-ranging applications. For example, such apparatus can be used in three important fields: optical computing, three-dimensional machine vision, and non-contact optical inspection. In optical computing, parallel individually-modulated light beams carry information through mathematical operations and deliver very fast and inexpensive solutions to complex problems heretofore solvable only using electronic supercomputers and massively-parallel specialized electronic processors. An optical computing method for accomplishing optical logic operations is described in U.S. Pat. No. 5,093,802 to J. N. Hait. Generation of the beamlet array for optical computing is accomplished in a variety of ways. For example, beamlet arrays for optical computing have been generated using a monolithic array of lenslets, fabricated using advanced lithographic and micromachining techniques; using holograms of lenslet arrays; or using a computer-calculated mask of an optical phase pattern.
For three-dimensional machine vision and non-contact inspection, a beamlet array is used to project a structured light pattern onto the surface to be measured. For example, U.S. Pat. No. 4,948,258 to Caimi discloses an apparatus for mapping a surface by passing a laser beam through a holographic grating structured to project a two-dimensional array of beamlets onto a surface, and then using a video camera to record the image of the beamlets reflected from the surface. The holographic grating is constructed using an array of lenslets. Other applications are described in "Three-Dimensional Object Recognition from Range Images,?M. Suk et al., Springer-Verlag, N.Y. (1992).
Surface profiling systems, many of which use laser scanning, are now commercially available, including, e.g., Cyberware's Rapid 3D Digitizer Model 3030, Airgage Co.'s CADEYES, CyberOptics's CyberScan, View Engineering's Voyager 1000, Seatex's Spotscan, RVSI's HR-2000, Rodenstock's RM600, Precision International's CM3000, Pacific Precision Laboratories' VideoCCM, Optical Gaging Products' QSEE Turbo 200, Mechanical Technology's MTI-2000, Laser Design's 3D Laser Digitizing System, EIIS's MK VII 3-D Surface Profiler, ELOR Optronics' 3-D Non Contact Airfoil Measurement System and Imageware's Surfacer.
Array-based active structured light inspection systems are described in "The Numerical Stereo Camera," M. D. Altschuler et al., Proc. SPIE Vol 283, p. 15 (1981) and in "Laser Electro-Optic System for Rapid Three Dimensional (3-D) Topographic Mapping of Surfaces," M. D. Altschuler et al., Opt. Eng. vol. 20, p. 953 (1981). This system generates a beamlet array using a lens to make a laser beam diverge, a four-facet prism to generate four virtual sources, and a microscope objective lens to produce a demagnified real image of the virtual sources. A video camera records the reflection of the beamlet array off the surface to be mapped. The beamlet array passes through a spatial light modulator (SLM) so that the individual beamlets can be identified.
U.S. Pat. No. 4,523,809 to Taboada et al. discloses an apparatus for generating an array of laser beamlets using a single laser beam and a four-facet prism. Because the laser beam is diverging, the prism introduces high optical aberrations. The prism-based system also requires very stringent alignment, which in turn necessitates heavy and costly support structures.
N. Streibl, in "Beam Shaping with Optical Array Generators," J. Mod Opt., 36, p. 1559 (1989) discloses another apparatus for generating an array of beamlets from a single input beam, using a computer generated hologram (CGH). Computer-generated holograms are described in U.S. Pat. No. 4,998,787 to Caputi et al., which is incorporated by reference herein. This technique is most effective for arrays of no more than 256.times.256 beams. A CGH is a calculated holographic pattern printed onto a photosensitive medium such as photographic film using lithographic techniques.